The present invention relates in general to heaters such as a ceramic heater and sheath heater and more specifically to a heater such as a glow plug for assisting start of a diesel engine and a water heater for heating coolant of an engine. The present invention further relates to a method of producing such a heater.
Heretofore, for the purpose of quickly starting a diesel engine, glow plugs have been installed on a cylinder block for pre-heating air within respective combustion chambers.
A conventional glow plug of the above-described kind is shown in FIG. 10. The glow plug includes a rod-shaped ceramic heater P4 having a sintered ceramic body P3 in which lead wires P1 and heating element P2 are embedded.
On the ceramic heater P4 is fitted a metallic tube P5 on which is fitted a metallic shell P6 which is to be fixed to a cylinder block. To the rear end (upper end in FIG. 10) of the metallic shell P6 are attached an insulator P7 and a round nut P13. Inside the metallic shell P6 are disposed a spring-shaped external connecting wire P8 connected to the ceramic heater P4 and a rod-shaped terminal electrode P9 connected to the external connecting wire P8.
The terminal electrode P9 has a protruded rear end portion protruding from the metallic shell P6 and having a threaded section P10 onto which is screwed a nut P11. The nut P11 cooperates with the insulator P7 to interpose therebetween a power supply metallic member P12 in the form of an elongated plate and hold it tightly therebetween. By applying a voltage across the power supply metallic member P12 and the metallic shell P6 (by way of the cylinder block), the ceramic heater P4 is caused to conduct and generate heat.
Cylinders of the diesel engine are provided with such glow plugs, and the power supply metallic member P12 is disposed so as to interconnect the protruded rear end portions of the terminal electrodes P9.
In these days, in order to prevent the exhaust gas emission of the engine from becoming worse, it is required to check the deterioration in performance of the glow plugs. However, the conventional glow plugs cannot suitably meet the requirement due to its structure.
For example, if the performance of each glow plug can be checked by OBD (On-Board Diagnosis) by using a test terminal connected to a microcomputer, the glow plug can be checked with ease. However, heretofore, the single power supply metallic member P12 has been used for supply of power to the glow plugs, so that it has been impossible to check the performance of each glow plug with ease.
Namely, in order to check the performance of each glow plug, it has been required to remove the power supply metallic member P12 and bring the terminal electrode P9 of each glow plug into contact with the test terminal, resulting in the necessity of a difficult work.
It is accordingly an object of the present invention, to provide a heater adapted to be able to check its performance with ease, i.e., by on-board diagnosis.
It is another object of the present invention to provide a heater and connector assembly which enables a heater to be checked by on-board diagnosis.
It is a further object of the present invention to provide a method of producing a heater of the foregoing character.
According to an aspect of the present invention, there is provided a heater comprising a metallic shell, a heating element disposed at an end of the metallic shell, and a terminal electrode partially disposed within the metallic shell and electrically connected to the heating element, wherein the terminal electrode has a protruded portion protruding from the metallic shell, and the protruded portion of the terminal electrode has a locking engagement section lockingly engageable with a connector for electrically connecting the terminal electrode to an outside for conduction of the heating element.
According to another aspect of the present invention, there is provided a heater and connector assembly comprising a heater having a metallic shell, a heating element disposed at a front end of the metallic shell, and a terminal electrode partially disposed within the metallic shell and electrically connected to the heating element, the terminal electrode having a protruded portion protruding from the metallic shell, the protruded portion of the terminal electrode having a locking engagement section, and a connector for electrically connecting the terminal electrode to an outside for conduction of the heating element, the connector being hollow and having a locking engagement section that is lockingly engaged with the locking engagement section of the terminal electrode thereby preventing axial movement of the connector relative to the terminal electrode.
According to a further aspect of the present invention, there is provided a method of producing a heater having a metallic shell, a heating element and a rod-shaped terminal electrode for electrically connecting the heating element to an outside for conduction of the heating element, comprising the steps of preparing an inner pole member and a terminal member which have joining portions one of which is hollow so that the other of the joining portions can be fitted in said one of the joining portions, fitting the other of the joining portions in said one of the joining portions, caulking the joining portions thereby joining the inner pole member and the terminal member together to constitute the terminal electrode, and disposing the terminal electrode in place within the metallic shell.